1. Field of the Invention
The present invention relates to systems and methods for coupling accessories to an engine/motor.
2. Background Art
Devices attached to the front-end accessory drive (FEAD) of an engine/motor in a vehicle consume power that could otherwise be directed to motoring the vehicle. Typical accessories may include a power steering pump, water pump, alternator, air conditioning compressor, air compressor, power-take off (PTO) drive, air for an induction blower, or a supercharger, for example. Various engine/motor accessories may be engaged/disengaged based on a request from the vehicle operator and/or the engine/vehicle controller in response to current ambient and vehicle operating conditions. However, each device is generally controlled independently of the state of other devices.
In automotive applications, electromagnetic friction clutches are often used to selectively engage various belt-driven FEAD devices. During engagement these clutches use an electrically controlled magnetic field to bring opposing frictional disks or plates into contact, which creates a rapid transfer of angular velocity to the driven clutch plate(s) that may result in undesirable noise, vibration, and harshness. In addition, the rapid transfer of torque to the engaged device often creates a rapid and noticeable diversion of torque from powering the engine and transmission. In addition, wearing of the frictional surfaces during engagement will eventually reduce the torque transfer capacity of the device.
More recently, magnetic powder or magnetorheological (MR) fluid clutches have been used in various automotive applications. Magnetic powder or MR fluid clutches have various advantages over electromagnetic friction clutches including the ability to operate in a slip or partial engagement condition, particularly during engagement and disengagement. This reduces the instantaneous power drop (stumble) or power increase (surge) in the engine, which also reduces the level of noise and vibration generated during engagement. While, magnetic powder or MR fluid clutches have been used to selectively couple an engine accessory to the FEAD as disclosed in U.S. Pat. No. 6,290,043 (air conditioning compressor); U.S. Pat. No. 6,619,413 (supercharger); and U.S. Pat. No. 6,173,823 (cooling fan), various engine/vehicle ambient and operating conditions exist where it may be advantageous to coordinate control of multiple or all FEAD devices, such as during vehicle acceleration events, transmission upshift/downshift events, cruise control, high engine speed events, cold-start events, etc.